BRIEF [O.A.] Willkomm-Schneider, Martha Author: Willkomm-Schneider, Martha Recipient: Haeckel, Ernst Dating: 16.10.1906
BRIEF OHNE UMSCHLAG Willkomm-Schneider, Martha Author: Willkomm-Schneider, Martha Recipient: Haeckel, Ernst Dating: ??.02.????
BRIEF [O.A.] Willkomm-Schneider, Martha Author: Willkomm-Schneider, Martha Recipient: Haeckel, Ernst Dating: 23.02.1911